Cant tell if serious.
If so, then wear one because its smart, my friend hit his head on a rock and got 15 stitches not wearing his helmet. He had worn it the entire day then took it off for the last run down, when it happened. He's alright, but was a scary situation.
I guess, moral of the story is you never know when something can go wrong, and as much as you think you are prepared your not. The dome piece is so important. I started this year with no helmet because I thought it was cool, but after that ^ happened I've worn mine almost everyday.